This invention relates to a semiconductor substrate and a method of manufacturing the same. The "semiconductor substrate" in this invention shall generally term a semiconductor wafer which has been cut out of a semiconductor crystal rod; a semiconductor device substrate which has become a device substrate for a single semiconductor device, a semiconductor integrated circuit or the like in such a way that after fabricating semiconductor devices on the semiconductor wafer (of course, a case of providing an epitaxial layer on the wafer and forming semiconductor devices in the epitaxial layer is naturally included), the wafer has been split into chips; etc.
In general, the epitaxial layers of silicon (Si) etc. exhibit inferior qualities of crystals, which form a major cause for lowering the manufacturing yield of devices. In order to reduce crystal defects in the epitaxial layer and to attain a good crystal quality, it is necessary to lessen contamination with heavy metals from outside, especially from a gaseous system, and to use a semiconductor substrate material such as Si having a small number of crystal defects. Further, the gettering process is important by which heavy metals or crystal defects originally existent inside the substrate are collected to a part not used for a device, for example, the rear surface of the substrate.
Ordinarily, the gettering is carried out by methods (1) wherein an impurity is diffused into the rear surface of a wafer, (2) wherein a high-density crystal defect layer is formed by implantation at a high density, (3) a damaged layer is formed in the rear surface by a mechanical working such as lapping, etc. Since, however, the methods (1) and (2) are conducted in the processes for manufacturing semiconductor devices after having purchased the semiconductor wafers of Si etc., one step increases, which unfavorably leads to a high cost. Regarding the method (3), there are such disadvantages that the control of the thickness of the damaged layer is difficult and that the damaged layer disappears mostly due to one heat-treatment in the process for manufacturing a semiconductor device, so the gettering effect is weak.